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SRI International's AIC Utility Library (for Java 1.6+)
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/*
 * Copyright (c) 2013, SRI International
 * All rights reserved.
 * Licensed under the The BSD 3-Clause License;
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at:
 * 
 * http://opensource.org/licenses/BSD-3-Clause
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 
 * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 * 
 * Redistributions in binary form must reproduce the above copyright
 * notice, this list of conditions and the following disclaimer in the
 * documentation and/or other materials provided with the distribution.
 * 
 * Neither the name of the aic-util nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, 
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 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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 */
package com.sri.ai.util.functionalsequence;

import java.util.LinkedHashSet;
import java.util.Set;

import com.google.common.annotations.Beta;

/**
 * A basic abstract implementation of {@link Refiner}. Extensions only need to
 * implement {@link #refineOrNull()}, which must return either a refinement of
 * the current value (available at {@link #currentValue}), or null
 * if that is not possible.
 * 
 * {@link #refineOrNull()} can choose to set {@link #knownToBeOver} if it
 * determines that no further refinements in the future will be possible even if
 * the present invocation of {@link #refineOrNull()} was successful. This will
 * avoid unnecessary subsequent calls to {@link #refineOrNull()} (the flag is
 * set automatically if {@link #refineOrNull()} fails).
 * 
 * @author braz
 * 
 * @param 
 *            the type of the value being computed.
 */
@Beta
public abstract class AbstractRefiner implements Refiner {

	protected boolean     knownToBeOver       = false;
	protected T           currentValue        = null;
	private   Set